After sugar is extracted from prepared cane, the resultant mixed juice (water, sucrose and other impurities) needs to be clarified. In the production of white sugar, this clarification is important as the better the clarification of the sugar juice, the better (i.e., more white) the final sugar will be.
The coagulation of the impurities in this stream is very important in achieving a good end product. After the clarification stage, the evaporation stage takes place. Any impurities present causing color problems in the liquid also get concentrated in the same proportion as the sugar juice does. Color levels of up to 6,000 to 10,000 ICUMSA color units are often obtained in this stage.
As such, a majority of sugar mills will clarify the sugar syrup after the evaporation stage. This process is typically accomplished by pre-coagulating the sugar syrup and passing it through a flotation system.
If phosphoric acid is used as the phosphate source in the pre-coagulation step, lime or calcium sacharate is used to neutralize this and maintain the pH of the sugar syrup in the neutral range to avoid sugar inversion.
This neutralization step can be a complicated operation due to solids level content. Sugar syrup can have 60 to 70% solids content and these can deposit over the pH meter's electrodes reducing its sensitivity and causing pH variations. These variations in pH can cause the color of the clarified syrup to be higher than before the clarification step. This substantially compromises the quality of the final sugar.
Additional complications arise due to the sugar syrup's high concentration. This high concentration causes lime dissolution to be slow and the pH adjustment will take more time to happen. This slow response will cause an overfeed of lime or calcium sacharate which in turn will cause a pH increase to levels other than the correct one and will result in high color and high ash content in the final sugar product.
Further difficulties can arise when this syrup is then passed to the evaporator systems. These systems are usually in a series of vessels each of which has a greater vacuum than the previous one. This process will concentrate the sugar juice even further. The use of phosphoric acid and other phosphate compounds in the clarification stage can cause scaling problems in the evaporation stage. The high phosphate concentration, when concentrated even more in the evaporation stage can crystallize and precipitate out causing deposition in the evaporative stage.
The present inventors have discovered a novel precoagulant composition that reduces the amount of phosphate employed and reduces the amount of scale formed in the evaporation stage of the sugar making process.